The present invention relates generally to a metal line of a semiconductor device and a method for forming the same, and more particularly, to a metal line of a semiconductor device that can improve the characteristics of a diffusion barrier and can thereby improve the characteristics and the reliability of a semiconductor device and a method for forming the same.
Generally, in a semiconductor device, metal lines are formed to electrically connect elements or lines to each other. Contact plugs are formed to connect lower metal lines and upper metal lines to each other. In order to conform to the trend towards highly integrated semiconductor devices, a design rule has decreased. Because of the decrease in the design rule, the aspect ratio of a contact hole in which a contact plug is formed has gradually increased. As a result, the difficulty of forming a metal line and the importance of a process for forming the metal line and the contact plug have received great attention from designers.
Aluminum and tungsten have been mainly used as the material for the metal line of a semiconductor device, since these materials have good electrical conductivity. In addition, copper has recently been recognized as having potential as a next-generation material for a metal line due to the excellent electrical conductivity and low resistance of copper when compared to aluminum and tungsten. Copper (Cu) has been recognized as potentially solving the problems associated with RC signal delay in a semiconductor device having a high level of integration and high operating speed.
Since copper cannot be easily dry-etched into a wiring pattern, a damascene process is employed to form a metal line of copper. In the damascene metal line forming process, a metal line forming region is formed by etching an interlayer dielectric, and a metal line is formed by filling a copper layer in the metal line forming region. The types of damascene processes can generally be divided into a single damascene process and a dual damascene process.
Where applying the damascene process, in a multi-layered metal line, an upper metal line and a contact plug for connecting the upper metal line and a lower metal line can be simultaneously formed. Also, surface undulations that are produced due to the presence of the metal line can be removed, and therefore a subsequent process can be conveniently conducted.
Further, when using copper as the material for the metal line, unlike the case in which aluminum is used, copper diffuses to a semiconductor substrate through the interlayer dielectric. The diffused copper acts as deep-level impurities in the semiconductor substrate made of silicon and induces leakage current. Therefore, it is necessary to form a diffusion barrier at an interface between a copper layer and the interlayer dielectric. Generally, the diffusion barrier is made of a TiN layer, a Ta layer or a TaN layer.
However, in the conventional art as described above, when manufacturing an ultra-highly integrated semiconductor device below 40 nm, the characteristics of the diffusion barrier made of any one of the TiN layer, the Ta layer and the TaN layer are likely to deteriorate, leakage current is likely to be induced, and contact resistance is likely to increase, whereby the characteristics and the reliability of the semiconductor device can be degraded.